How To Remove Bluing From Steel

Removing bluing from steel

Bluing is a chemical method of
protecting steel from rusting.
It's a form of passivation, the electrochemical
creation of a thin outer shell of protective material.
In the case of blued steel, the protective layer is
magnetite or Fe3O4,
a black oxide of iron.
Bluing provides just partial protection against rust,
you still have to be very careful to apply oil to the
surface.
Bluing has been a traditional protective treatment for guns.
Parkerizing
provides better protection against both oxidation and wear.
It requires less day-to-day maintenance and so it is
more attractive to the military.
So, you may want to remove the bluing from your guns
in preparation for
parkerizing.

First, some warnings

This is not
the
way to remove bluing from steel, but it is
one
way to do it.
It might work for you.
I'm no metal-treating guru.

CAUTION:
Technical data and information contained herein are intended
to provide information based upon the limited experience of
individuals under specific conditions and circumstances.
They do not detail the comprehensive training, procedures,
techniques and safety precautions which are absolutely
necessary to properly carry out similar activity.
Always consult comprehensive reference manuals for
details of proper training requirements, procedures,
techniques and safety precautions before attempting
any similar behavior.

OK, that should be enough lawyer repellent...

Some background on Bluing

Bluing
is an electrochemical passivation process
to partially protect steel against rust.
That's
electrochemical
as in chemical reactions which take place in a solution
at the interface of
an electron conductor (a metal or a semiconductor)
and an ionic conductor (the electrolyte),
and which involve electron transfer between
the electrode and the electrolyte or species in solution.
It does not mean that electrodes and wires
are involved at all!

Of course those are cases and not bullets.
Cats are notorious for their poor grasp of
technical terminology, not to mention their
typing and English grammar....

Passivation is the formation of a thin non-reactive
surface film inhibiting further corrosion.
Bluing is therefore the oxidation of the surface of
the steel, oxidation in a form preferable to the
oxidation of rust.
The name comes from the resulting very dark color,
really more black than blue.

Rust is Fe2O3,
a red oxide that occupies more volume per iron atom
than iron itself.
That slight space differential causes
the typically reddish rusting away of iron.
You might think of the iron as levering itself away in tiny
Fe2O3
particles from the main body.
See the Wikipedia articles on
rust
and
corrosion
for examples of catastrophic structural failures
caused by rust build-up forcing apart adjacent parts,
sometimes called "rust smacking".

How can Fe3O4 occupy the same space as
just plain old Fe?
Don't those extra oxygen atoms have to also bulk up the
material as with Fe2O3 or rust?

No, because atoms are mostly empty space.
The density in iron atoms per volume will depend on the
shape, size, and interaction of the electron orbitals,
which are really electron probability density functions.

On the other hand,
magnetite is Fe3O4,
a black oxide occupying the same volume per iron atom
as iron itself.
A chemical reaction called "bluing"
can form an outer layer of magnetite
and provide minimal protection against corrosion.
The treated steel must be coated with a thin film of
oil, and the bluing is not resistant to wear and is
typically no thicker than 0.0001 inches.

Hot bluing is typically done by immersing the parts in
a solution of potassium nitrate (KNO3),
sodium hydroxide (NaOH),
and water heated to the boiling point.
Yes, boiling lye, be very careful.

Cold bluing is less effective, and is used mainly for
cosmetic touch-up work.
Some cold bluing solutions contain
selenium dioxide (SeO2).

Parkerizing
is another electrochemical method
of protecting steel from corrosion,
and it also increases resistance to wear.
Parkerizing is the creation of an
iron-phosphate conversion coating
on the outer surface of the steel,
producing a grey matte finish.

There are several related techniques, but generally
they involve a phosphoric acid solution with key
ingredients of zinc or manganese, with varying amounts
of nitrates, chlorates, and copper, the solution being
heated to 88-99°C, close to the boiling point.
So, instead of the boiling lye of bluing,
parkerizing uses boiling acid.
It's nasty at the opposite end of the pH scale.

Different metal salts in the solution produce different colors
of non-reflective finish:

Zinc

Light to medium grey

Manganese

Light to dark grey, or black

Iron

Dark grey to black

Phosphating, interacting with a coating of cosmoline over
several months to years, may produce a light
greenish-grey color.

On To The Project

Norinco
corporation applies a nearly black and sometimes
uneven bluing to their products, like this
M1911A1
slide.
Parkerizing should provide a more protective finish,
and most any finish would be more attractive than this.

These photographs show the pieces on a sheet
of white paper.
See, it's nearly black.
Maybe some brown, very little sense of it being blue.

Clean off all the oil.
Something like brake cleaner (basically a compressed
spray of hydrocarbon solvents) would do an excellent
job.
Common drug store isopropyl alcohol in a spray pump
bottle may be good enough to get the job done,
even though it's 30% water.

Here is the active bluing-removal agent —
white vinegar.
See, bluing isn't all that protective after all.
This is marked as being distilled and then diluted
to 5% acidity.

How did I come up with the crazy scheme of
dunking precision machinery in vinegar?

I saw a number of postings to various on-line gun
forums where people reported doing this.
The one that I most remember was from a guy who
discovered that vinegar removed bluing when the
Taco Bell hot sauce dripped onto his gun because,
no joke,
he was going to the range and carrying his gun
and some tacos in the same paper bag.
When he got to the range and discovered the mess,
he wiped off the hot sauce and saw that the
bluing came with it.

The not-so-sophisticated bluing removal chemical.

His unorthodox and rather inappropriate
carrying method certainly got my attention.
I will keep my tacos and my pistol in separate bags,
but at least we can learn from his observational chemistry.
Taco Bell sauce lists vinegar as a primary ingredient.

All the blued parts that will eventually be parkerized
have been disassembled, cleaned, and placed in
a glass dish.

Then pour in enough vinegar to completely submerge
all the parts and wait.
The bluing started to come off
after just about 15 minutes or so.

The blued M1911 parts have been placed in a glass dish and
covered with vinegar.
It's nearly impossible to see in this image that all the
parts are completely submerged in the clear liquid.

The outermost layer of blued steel is converting from
magnetite, or Fe3O4,
to rust, or Fe2O3,
after about 20 minutes in the vinegar bath..
Again, these parts are completely submerged in clear vinegar
although it's almost impossible to tell in this image.

The frame has turned orange-brown after maybe 20 minutes.

Not entirely — see the patches still nearly black
at lower left.

I think that what's happening here is that the
acetic acid in the vinegar is converting the very thin
outer layer of black magnetite to the orange iron oxide
of rust.

So what if it ends up being 0.0001" smaller — Norinco
fabrication standards are far looser.

You can't really see it here but these parts are
submerged in vinegar.
The vinegar is clear and only shows up in this picture as
the reflection of the flash at lower left.

Remove each part every 20 minutes or so and wipe it
down with a paper towel to remove the lifted oxidation.
Then place it back in the vinegar bath.

The orange-brown oxide starts to come off as you
handle the parts.

The parts were removed and wiped with a paper towel every
15 to 20 minutes until they were all "in the white" or
without bluing.
The rust starts coming off as soon as you touch the parts.

M1911 frame and slide with all bluing removed.
The slide needs further wiping to remove rust.

There seemed to be bare metal everywhere after two hours.
Remove the parts, pour out the vinegar, and place
the parts back in the dish.
Then place the dish under a slowly pouring faucet for
several minutes to flush the vinegar.

Follow that with further careful flushing of each piece
and hand drying.

The M1911 frame and slide have been rubbed with extra fine
steel wool and a light coating of gun grease rubbed onto
the surface to protect against rust until the parts can
be bead blasted and then parkerized.

You can heat an oven to 250°F or 120°C
and place the parts inside for about 20 minutes
on a pan lined with aluminum foil.

The heat will dry the parts and leave some light
orange rust deposits.

The next step is to rub any light orange rust deposits
with extra fine steel wool.
Then apply a thin film of gun grease.

WARNING: All content on this web site, including technical data,
information, and reports of any activities, do not detail the
comprehensive training, procedures, techniques, and safety precautions
which are absolutely necessary to properly carry out similar activity.
The reader MUST NOT attempt any reported activity, technique, or
use of equipment based on reports on this web site.
Always consult comprehensive reference manuals for details of
proper training requirements, procedures, techniques and safety
equipment and precautions before attempting any similar behavior.